1. Field of the Invention
The present invention provides a transmission circuit and related method, and more particularly, a transmitter circuit and related method compensating and emphasizing the quality of the transmission signal with equivalent capacitance effect.
2. Description of the Prior Art
In modern society, every kind of information, such as data, documents, and video files are able to be transformed into electronic signals. How to quickly and correctly transmit electronic signals for information circulation with more efficiency has also become the target of the research and development of modern information companies. For instance, in the electronic systems or network systems, data exchanging between different functions of circuits, devices, and terminals is accomplished by buses or network transmission lines for coordinating the operation, which realizes the entire function of the electronic systems or the network systems. Therefore, raising the efficiency of the signal transmission between circuits, maintaining the quality of the signal transmission, and lowering the power dissipation of the signal transmission contribute to the rise of the entire efficiency and the performance of the system.
Generally, when a transmission circuit in the system transmits signals to a receiving circuit by a connection (bus, network transmission lines), the transmission circuit inputs the ready-for-transmission signals into the transmitter which drives the ready-for-transmission signals (input signals) into output signals transmitted to the receiving circuits. In the prior art, the transmitters are formed of CMOS transistors, and the CMOS transistors conduct or close according to the level of the input signals to push/pull the output signals. Since the CMOS transistor can be an inverter and there is inverse trend between the input/output signals, the inverse trend will cause the charge injection and clock feed-through. The charge injection and clock feed-through form a rising peak wave in the falling-edge of the output signal or a falling peak wave in the rising-edge of the input signal and interfere with the normal level transition of the output signal.
However, as known by those skilled in the art, the natural characteristics of the connection (the connection length and the equivalent output impendence and load of the connection) and the signal itself (the levels of frequency and clock) affect the quality of the signal transmission and the signal distortion of the receiving circuit. For instance, the transmission circuit transmits a signal of a square wave to the receiving circuit, but in fact, the receiving circuit receives the square wave whose rising and falling edges become slack during the transmission, making the original square wave distort into a sawtooth wave so that the recognition of the signal of the receiving circuit is affected.
In the prior art, to improve the bad transmission characteristics, two transmitters and a clock delay circuit are used in the transmission circuit to pre-emphasize the wave of the output signal for emphasizing the amplitudes of signal changes at the rising and the falling edges of the signals in the output signals, thereby reducing the wave distortion during transmission. However, there are disadvantages of the prior art. First, the technique of the prior art uses two transmitters to synthesize one emphasized output signal, which increases power dissipation and layout area used. Second, in the prior art, the emphasized signal is properly synthesized with a clock delay circuit which needs an extra clock to trigger. Furthermore, the transmitter of the prior art is interfered with by some non-ideal factors, e.g. charge injection and clock feed-through. Even by using two transmitters matched with a clock delay circuit to synthesize emphasized signals, due to the non-ideal factors in the synthesizing process, the ideal emphasized signals cannot be synthesized by the prior art.